This invention relates to a metal container, such as a light-gauge metal container, having a closure flange, adapted to receive a threaded plug, fixed on a container wall. More particularly, it relates to an apparatus for fastening the closure flange to the container wall.
Most of larger-capacity, e.g., 5 gallons and above, light-gauge metal containers have openings in a container wall to get the contents and air in and out. Each opening carries a closure flange into which a threaded plug is screwed. FIG. 1 shows a steel drum. A top head 2 fixed to a body 1 is fastened with a bung flange 3 and a vent flange 4, with both flanges screwed with threaded plugs 5 and 6. The following description will be made with reference to a steel drum carrying closure flanges on the top head.
According to a conventional method disclosure by U.S. Pat. No. 3,863,800, for example, a cylindrical closure flange neck is fitted in an opening neck on the top head. The closure flange is fixed to the top head by outwardly curling the uppermost end of the flange neck. Sealing is effected by inserting a gasket between the two necks. Another method according to U.S. Pat. No. 3,393,823 double seams top head opening and cylindrical closure flange necks, with a gasket interposed therebetween.
The closure flange thus fastened to the top head by curling or double-seaming may loosen when a shock is given to it during the transportation or handling of the drum or the plug is screwed in with excess force. Some materials contained in the drum may erode the gasket, which results in leakage of the contents. Not going so far as to cause leakage, the dissolved gasket may contaminate or deteriorate the contents.
To solve these problems, or to provide adequate strength demanded of containers for radioactive substances, some drums have the closure flange welded to the top head, as shown in FIG. 2. As seen, a top head 9 of a drum 8 has an opening to receive a closure flange 13, with the edge of the opening leveled off. The lower portion of a cylindrical body 14 of the closure flange 13 is inserted in the opening. The bottom surface 15 of the inserted body and the lower (internal) surface 10 of the top head 9 are flushed. Welding 18 is given along a circular seam 16 at which the circular surface of the opening in the top head 9 and the lower periphery of the closure flange 13 contact.
The top head 9 with this closure flange 13 has the flattened opening edge, with the lower surface of the top head and the bottom surface of the closure flange flushed with each other. Accordingly, excess stress may cause a leaky crack in the vicinity of the seam 16. Also, welding heat may deform the entire closure flange to impair the fitness of the threaded portion.
According to another welding method, fillet welding 19, indicated by a dot-dash line in FIG. 2, is given to join the upper surface 11 of the opening edge in the top head 9 to the periphery of an annular projection 17 on the closure flange 13. This structure also involves the same defects as the preceding one. What is worse, the increased welding length increases not only the welding cost, but also the incidence of such defects and the intensity of their effects.
Metal containers usually are mass-produced (for example, one plant manufactures 100-thousand drums monthly), on the automatic assembly line. It is therefore desirable that welding of the closure flange to the drum body be incorporated in the manufacturing line. To permit this incorporation, it is essential that high-quality welding parts be used, welding position determined quickly and accurately, welding completed in a short time, and welding operation automated readily.